In the related art, it is desirable to carry out inspection and management of the air pressure in a pneumatic tire (simply referred to below as a “tire”) assembled on a vehicle in terms of improving the durability of the tire, improving the wear resistance, improving the fuel consumption, or improving the comfort of the ride, in addition to improving the maneuverability. Therefore, various systems for monitoring air pressure of tires have been proposed. Generally, in these systems, air pressure in tires is monitored by detecting the air pressure information of a tire assembled on a wheel, providing a transmitting device for transmitting this information in a tire hollow region of each of the wheels, and acquiring the air pressure information of each tire from the transmitting devices.
For example, a transmitting device and a system are known which are able to appropriately measure and acquire tire information such as the air pressure information of the tire even when repairing a puncture of the tire using a puncture repairing liquid (see Japanese Unexamined Patent Application Publication No. 2011-105083A). Specifically, the transmitting device has a sensor which detects, as tire information, a state of a gas which is filled in a hollow region of a tire which is surrounded by the tire and a rim, a transmitter which wirelessly transmits the detected tire information, and a casing which covers the sensor and the transmitter. The surface of the casing is provided with an aperture part which connects the space inside the casing and the tire hollow region, and the aperture part is provided at the apex of a protruding part which protrudes from the surface of the casing in one direction. The height of the protruding part is 1 mm or greater and the surface area of the aperture part of the through hole is 0.4 mm2 or less.
For example, a puncture repairing liquid which is introduced into the tire hollow region interposed between the tire and the rim is used when the tire is punctured. However, since the aperture part which connects the space inside the casing and the tire hollow region is provided at the apex of a protruding part which protrudes from the surface of the casing in one direction, and the height of the protruding part is 1 mm or greater, even when the puncture repairing liquid is attached to the transmitting device provided in the tire hollow region, it is difficult for the puncture repairing liquid to attach to the apex of the protruding part. Furthermore, since the surface area of the aperture part is also small, it is considered that there are no problems in terms of the ventilation holes being blocked or the measuring of the air pressure being influenced.